Today, more than ever, the demand on coating performance has increased to where the coating application has become paramount in the operational functioning of the coated structure. In the past, structural coatings were applied as a means to prevent corrosion and increase the aesthetic appearance of the coated structure. The requirements of coating performance are no longer limited to the obvious aesthetic value and corrosion resistance. Today coatings are required to take on a multifunctional role, typically, new coatings are also used to enhance UV resistance, abrasion resistance, and chemical resistance.
Of particular interest to our transportation infrastructure are electrically heated layers covering particular regions of the aircraft's or ship's substrate. In the past, such electrically heated structures were laminated between layers of safety glass or other optically transmissive materials. These heaters (which are used on ships, aircraft, and automobiles) prevent ice buildup and increase visibility by removing condensation. U.S. Pat. No. 6,832,742 describes a system and method for electrical de-icing coating. This patent describes a composite material with an electrical mesh connected to a voltage source; this is to enable the removal of ice buildup on aerospace or other transportation vehicles. This patent describes a method for manufacturing such a composite layer. Also in this patent, is a method described from mechanically affixing the composite layer to a substrate. This is accomplished by using common industrial adhesives.
U.S. Pat. No. 4,737,618 describes a “heating element for a defrost device on a wing structure, such a device and a process for obtaining same”. This patent describes electrical resistive elements in a device, such as a wing structure of an aircraft, or the blades of a helicopter, that includes conductive fibers embedded in a composite matrix structure, and power supply wires connected electrically to the said conducting fibers. These include carbon fibers oriented in the shape of a ribbon that are preimpregnated with resin and affixed to a substrate layer. These electrical resistance elements are then soldered to a corresponding power supply.
For many years the buildup of ice on transport vessels and vehicles has long been understood as a persistent problem. In fact, such ice buildup has been a major cause of the loss of life and loss of revenue for transport companies and individuals. Generally speaking, ice buildup occurs in two fashions, rime ice, and clear ice. Rime ice occurs when nearly frozen particles come in contact with the structure that is near, or at, the freezing point. The freezing particles begin to form a buildup of ice on the structure. Rime ice tends to be more detrimental for laminar flow on aircraft, because rime ice is very rough in its nature. Clear ice forms when super cooled water droplets come in contact with a surface that is at, or below, the freezing point. Clear ice is more insidious in nature, because its formation is not easily recognized by visual inspection in-flight. However, the weight produced by clear ice can build up rapidly. This is not only true for aircraft, but for ships as well. The effect of ice accumulation is even worse on rotational components, such as propellers and helicopter rotor blades. De-icing equipment should be activated on these components prior to its accumulation. This means that icing conditions must be anticipated. However, if these conditions are not anticipated and icing is then unexpectedly encountered, a dangerous situation can occur. The application of de-icing equipment at this point can lead to a severe, out of balance condition. This is because current de-icing technology cannot shed equal amounts of ice on opposite sides of the rotating mass. To make this problem even worse, when the ice finally breaks free, it is sent crashing into other structures, sometimes causing severe damage. Different types of devices are known for de-icing in these critical zones on aircraft and ships. The majority of these “critical zone” devices employ electric heating as a means to break the ice free structure. Aircraft often use bleed air from the turbine engine to melt the ice by ducting bleed air in channels beneath the structure. Ships will often employ steam or hot water, in concert with electrical power, to remove ice. An additional technique, to remove accumulated ice is with the use of chemical de-icing agents, such as alcohol and propylene glycol. All the associated techniques are burdened with cost, both monetary and in the performance of the transport body. For example, the typical cost of the de-icing of commercial aircraft is in a range between $1500 and $3000. This is dependent on the size of the aircraft and the locale of the de-icing application. Chemical de-icing can be performed many times a day on a single aircraft, not only is the cost prohibitive, but the impact that these chemicals have on our environment is detrimental as well. Other de-icing techniques are more easily implemented by the ship and aircraft pilot. Even these techniques have their drawbacks. For example, using bleed air off turbine engines reduces available power for the aircraft and also increases the amount of fuel consumed.
Electrical de-icing equipment has many advantages, some of these are: they may be activated by the pilot or operator at will, or they may be controlled by an automatic system, such as a computer programmed device, which will eliminate the human factor in determining when the de-icing system must be activated. Current technology and electrical devices for de-icing consist of a network of resistive wiring elements. This is not unlike what one would find on the rear window defroster in an automobile. Even the state of the art electrical devices have these drawbacks. Metallic wiring elements are generally placed in a rubber matrix that is bonded to the leading edge of a wing, or that of a rotor blade, or propeller. The whole of this device is fragile and has a very short lifespan, especially when operated for significant amounts of time. Repair of this type of device can be very expensive and is not easily accomplished. In fact, when damage becomes apparent, the entire de-icing device is replaced.
Newer and more improved construction techniques are being developed. These generally include a pre-fabricated matrix that consists of the resistive metallic heating elements and a woven fiber support. This is generally covered with a rubberized coating or compatible plastic material. The ends of the metallic heating elements are connected to a suitable power supply. The power supply's electrical current is modulated in a predetermined fashion. A large part of the electrical heating elements are connected in series with each other. Although many of these arrays may be connected in parallel, it still stands to reason that if one element line fails, it will cause the subsequent failure of many sections connected electrically to the failed section. This can be disastrous in the case of a rotating structure, such as a propeller, or a rotor blade. The resulting out of balance condition has, and will cause, the disintegration of the rotating mass. Other factors that detract from current technique include the added mass of the de-icing system, coupled with the fact that they tend to disrupt the airflow around an aerodynamic body.